Ethylenediamine-N,N'-disuccinic acid ethylenediamine lyase is used as a catalyst for producing an optically active aminopolycarboxylic acid from fumaric acid and a compound having amino group. The thus-produced optically active aminopolycarboxylic acid has a specific property of capturing metal ions such as heavy metal ions. Moreover, the optically active aminopolycarboxylic acid is susceptible to biodegradation thus being expected of its use as, for example, a chelating agent, a builder for detergents and a bleaching agent for photographs.
The present inventors have previously found a novel microbial lyase activity that converts fumaric acid and ethylenediamine into S,S-ethylenediamine-N,N'-disuccinic acid (hereinafter, referred to as ethylenediamine-N,N'-disuccinic acid ethylenediamine lyase and abbreviated as EDDSase), and proposed a method for producing optically active aminopolycarboxylic acids efficiently from fumaric acid and different amines while utilizing the above-described catalytic action (see JP-A-9-140390 or U.S. Pat. No. 5,707,836). However, microorganisms possessing such EDDSase have fumarase too, which fumarase is widely present in the biological world and can hydrate most of the fumaric acid, i.e., a common substrate for EDDSase and fumarase, into malic acid. Unless the fumarase activity is removed from the microorganisms, it is difficult to obtain an optically active aminopolycarboxylic acid of interest in a satisfactory yield.
Examples of known methods for removing the fumarase activity are: a method in which a microorganism with aspartase activity is subjected to acid-treatment (see JP-B-3-55103); and a method in which a microorganism belonging to the genus Brevibacterium with aspartase activity is treated under alkaline conditions in the presence of L-aspartic acid and an ammonium ion (see JP-B-4-80678).
However, it was experimentally confirmed that the former method could not be applied to microorganisms with EDDSase activity since the loss of the EDDSase activity was greater than the loss of the fumarase activity during the treatment. The latter method is advantageous when employed for the production of L-aspartic acid wherein the microorganism to be treated is applied to the reaction system containing a large amount of L-aspartic acid, but the method was unfavorable in operability and economics for use in other reactions.
Since the EDDSase according to the present invention is an enzyme different from the above-described aspartase, it was unknown as to how to selectively remove the fumarase activity alone without loss of the EDDSase activity.